In the permanent mold casting of light alloy cylinder heads, it is common to use a plurality of permanent molds mounted on a turret, the molds being movable successively through a series of stations during which the molds are successively closed, filled, cooled, opened and unloaded. Such molds conventionally comprise a base and two movable platens sliding over the base. In order to permit setting of separate cores or ports in the cylinder head, it is conventional to divide the platen into upper and lower portions that are individually slidable relative to one another. Such an arrangement requires separate sets of guides for the relative sliding portions of the platens and more complex apparatus for moving the platen portions. Accordingly, one of the objectives of the present invention is to provide a more simplified mold construction which obviates the wear problems of prior art permanent molds and eliminates the need for complex operating mechanisms.
In the prior art permanent molds, it is conventional to cast the cylinder heads with the combustion chamber up in order to insure a better filling of molten metal. In such an arrangement, a removable top core is used having a plurality of downwardly extending portions defining the cylinder heads. The top core is subjected to heat distortion and, unless carefully controlled, may result in difficulty in maintaining the proper volumetric tolerances in the combustion chamber. Accordingly, another objective of the present invention is to provide a permanent mold having a novel top core construction which will insure the acceptable tolerances in the volume of the combustion chambers when the mold has reached the working temperature.
Further, in prior art permanent molds, the pouring basin or cavity and runner are generally obtained or provided in the area where the platen joins the bottom plate. In such an arrangement, it is difficult to avoid heat distortions and resultant gaps due to imperfect matching of the platen and bottom plate surfaces. Accordingly, another objective of the present invention is to provide a platen end construction which is independently movable and thereby can be adjusted to obviate the disadvantages of heat distortion.
In the prior art permanent molds, another problem occurs in connection with the movable metal cores that are required for spark plug holes, valve guides, rocking lever supports and the like. Such cores are usually mechanized by an actuator located along the center line of the metal core itself, each core or sets of cores having their own actuators. This arrangement has severe limitations because of the numerous actuators required to be associated with the mold. Accordingly, another objective of the present invention is to provide a permanent mold having a more simplified arrangement of movable cores.